The particles of Saturn’s rings, it appears, soar much further from their planet’s plane than scientists previously believed. This suggests the rings are more akin to a colossal dust donut.
Saturn’s rings themselves are very thin: they stretch tens of thousands of kilometers wide, but are only about 10 meters thick, creating an astonishing view of the planet when observed from Earth. However, there are deviations from this form—for instance, the looser outer E ring, which is fed by Saturn’s moon Enceladus, ejecting ice from its subsurface ocean.
Scientists analyzed data from the Cassini probe, gathered in 2017—the final year of the mission—the results of which were shared in The Planetary Science Journal. The craft then made 20 orbits in very steep loops through the rings, beginning its path up to three Saturn radii above its equatorial plane and plunging to a similar depth underneath it.
Cassini’s spectrometer—a cosmic dust analyzer—detected hundreds of minuscule stony particles at the highest point of the craft’s trajectory. Their chemical composition matches grains from the main ring, featuring low iron content.
“This is a completely unique spectral type that we do not encounter anywhere else in the Saturn system. Closer to the ring plane, there is far more material, but it is still surprising that we see these particles so far out—both above and below the ring plane,” says Professor Frank Postberg of the Free University of Berlin, one of the study’s authors.
According to scientists’ calculations, to ascend so high—more than 100,000 kilometers from the main ring—the particles must attain speeds exceeding 25 kilometers per second to overcome Saturn’s gravity and magnetic forces.
Dr. Postberg states that it is unclear what process could impart such velocity. The most straightforward explanation is impacts by tiny meteoroids with the rings, which scatter particles—but this is insufficient to produce such fast debris.
However, recent research indicates that micrometeoroids colliding with Saturn’s rings might generate temperatures adequate to vaporize rock. This work also posits that Saturn’s rings are much older than previously thought. Postberg and his colleagues surmise that the vaporized rock may exit the rings at speeds far greater than fragments, then condense at a vast distance from the planet.
The detection of dust so far from the main ring is surprising, reckons Professor Frank Spahn of the University of Potsdam—because ring particles are very tiny and rarely collide, and upon contact, they tend to stick together like snowballs rather than bouncing apart like billiard balls.
Collisions with micrometeoroids occur throughout the Solar System, so a similar process might be happening around other planets with rings, such as Uranus.
“If high-speed impacts on icy rings are a universal occurrence, then we should expect analogous dust halos above and beneath other rings,” Postberg concludes.
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